Friction pad pressing apparatus for use in disc brakes

ABSTRACT

A friction pad pressing apparatus for use in a disc brake adapted by a dual hydraulic braking system having first and second hydraulic pressure circuits. The apparatus comprises a first piston and a second piston which are slidably received in a cylinder and are each actuated by the hydraulic pressure supplied by said first and second hydraulic pressure circuits respectively, detent means for the second piston and resilient means for urging the second piston to abut with the first piston.

United States Patent [1 1 Ooka et al.

[ June 26, 1973 1 FRICTION PAD PRESSING APPARATUS FOR USE IN DISC BRAKES [75] Inventors: Toshiwo Ooka, Amagasaki; Koji Takata, Nishinomiya, both of Japan [73] Assignee: Sumitomo Electric Industries, Ltd.,

Osaka, Japan 22 Filed: Jan.29, 1971 21 App1.No.: 111,073

[30] Foreign Application Priority Data Feb. 4, 1970 Japan 45/10289 [52] U.S. Cl 188/345, 188/106 P [51] Int. Cl B601 11/20 [58] Field of Search 188/73, 106, 152,

[56] References Cited UNITED STATES PATENTS 3,490,565 Marschall et a1. 188/345 11/1969 Kobayashi 188/106 5/1958 Frayer 188/73 Primary Examiner-Richard E. Aegerter Assistant Examiner-Johnny D. Cherry AttorneyWil1iam D. Hall, Elliott I. Pollock, Fred C. Philpitt, George Vande Sande, Charles F. Steininger and Robert R. Priddy [57] ABSTRACT A friction pad pressing apparatus for use in a disc brake adapted by a dual hydraulic braking system having first and second hydraulic pressure circuits. The apparatus comprises a first piston and a second piston which are slidably received in a cylinder and are each actuated by the hydraulic pressure supplied by said first and second hydraulic pressure circuits respectively, detent means for the second piston and resilient means for urging the second piston to abut with the first piston.

4 Claims, 1 Drawing Figure FRICTION PAD PRESSING APPARATUS FOR USE IN DISC BRAKES The present invention relates to an improvement in friction pad pressing apparatus adapted for use in disc brakes.

Specifically, this invention relates to such a friction pad pressing apparatus that is adapted to be operated by a dual hydraulic braking system such as a braking system including a tandem master cylinder and separate two hydraulic pressure circuits connected to the cylinder and that is able to press friction pads against a rotating brake disc, even if one of the hydraulic braking circuits is impaired to an extent that the hydraulic pressure is no longer supplied through said circuit from the tandem master cylinder, through the other of the hydraulic braking circuits by substantially the same force as when none of the dual braking circuits is impaired.

Pressing apparatus of the type using dual hydraulic braking system has been disclosed in British Pat. No. 951,906. According to the apparatus disclosed in the above British patent, when one of the hydraulic pressure circuits is impaired, the pressing force of the apparatus has been reduced to half a value obtained when none of the hydraulic pressure circuits is impaired, and in addition, the volume of braking liquid required for the other of the circuits which is not impaired must be increased more than when none of the hydraulic pressure circuits is impaired.

An object of the present invention is to eliminate these defects as mentioned above. According to the friction pad pressing apparatus of the present invention, there are provided within a single hydraulic cylinder two pistons to which separate hydraulic pressure circuits lead respectively from'master cylinder in such a manner that the pressing forces acting respectively on these pistons due to the respective hydraulic pressures supplied by the associated hydraulic pressure circuits are substantially identical with each other. Therefore, even if only one of these pistons is urged to move the same pressing force acting to press the friction pads against the disc can be obtained through the other piston as when both pistons normally operate.

it should be noted that the important features of the improved friction pad pressing apparatus according to the present invention reside in that the first piston for directly pressing the associated friction pad against the rotating disc is normally forced to abut with the second piston, and the second piston is provided with detent means.

Being constructed as mentioned above, in the friction pad pressing apparatus of this invention, it is possible to prevent the undesirable displacement of the piston which occurs in the conventional apparatus of this kind due to the unbalance in hydraulic braking pressure caused when one of the hydraulic pressure circuits is impaired. Therefore, in the improved friction pad pressing apparatus of the present invention, it is possible to obtain the same braking effect as when none of the dual hydraulic braking system is impaired, without requiring additionally excessive braking liquid.

The objects and advantages of present invention will become more apparent from the following description made in conjunction with the accompanying drawing which shows a longitudinal sectional view of a friction pad pressing apparatus embodying this invention.

In the drawing, a pair of friction pads 2 and 3 are provided in opposed relation with each other on both sides of a disc 1 secured to a rotating member to be braked such as, for example, a vehicle wheel, and are adapted to be pressed against the disc so as to be brought into frictional engagement with the associated surfaces of I the disc.

A hydraulic cylinder 4 is disposed to the right-hand side of the pad 3 as viewed in the drawing, namely, at the side remote from the disc 1 so that the pad 3 is positionedbetween the disc 1 and the cylinder 4. (Hereinafter, it should be understood that the terms left and right refer to the direction as viewed in the drawing.) In the cylinder 4 there are provided a first piston 5 adapted to directly engage with the pad 3 and a second piston 6 positioned on the right-hand side of the first piston 5, that is, on the opposite side of the disc 1 with respect to the first piston 5. Within the hydraulic chamber 4, there is provided a liquid chamber 7 between the first and second pistons 5 and 6 to communicate with a first hydraulic pressure circuit of a dual hydraulic braking system connected to a single hydraulic pres sure source through a port 8 provided on the cylinder 4, while there is provided a liquid chamber 10 between the second piston 6 and the bottom 9 of the cylinder 4 to communicate with a second hydraulic pressure circuit of the aforesaid system through a port 11 provided on the cylinder 4.

Ports 12 and 13 communicating respectively with the chambers 7 and 10 are formed on the cylinder 4 for discharging therethrough the air contained in the liquid chambers 7 and 10 when the pressing apparatus is-assembled, and air-tightly sealed after completion of the assembling.

The hydraulic cylinder 4 is also provided at its bottom 9 with a cylindrical rod 14 liquid-tightly secured thereto and extending in the axial direction of the cylinder 4 into a bore 15 formed in the second piston 6 on the side thereof remote from the disc 1 but adjacent to the bottom 9 of the cylinder. The forward extremity of the rod 14 is loosely fitted in a guide recess 16 having the diameter slightly larger than that of the extremity of the rod 14.

The bore 15 includes the guide recess 16, an enlarged portion 17 of conical shape followed by the guide recess and a cylindrical portion 18 succeeding to the portion 17 and having a larger diameter than that of the guide recess 16. The enlarged conical portion 17 accommodates therein a plurality of balls 19 engaged by a ball stopper 20 which is slidably mounted on the rod 14 and biased by a spring 21 to the left in which direction the gap between the outer surface of the rod 14 and the inner wall surface of the conical portion 17 becomes narrower, whereby the movement of the second piston 6 is prevented.

Although the second piston can move to the left when fluid under pressure is applied to the chamber 10, it cannot move to the right when a first fluid under pressure is applied to the chamber 7, due to the increase of frictional force between the balls 19 and the outer surface of the rod 14.

Such a mechanism operable as mentioned above is one embodiment of the detent device in the present invention. It should be notedthat any known type of detent device may be employed in the friction pad pressing apparatus of the present invention, and the present invention is not restricted to only such a detent device as mentioned above.

The spring 21 is supported at its one end by an annular stop 22 rigidly secured to the second piston at the position of the open end of the bore 15 and is slidably fitted on the rod 14. I

The second piston 6 includes a projecting portion 23 extending toward the disc for pressing the first piston. This projecting portion 23 is inserted in a bore 24 formed in the first piston and the head of said projecting portion 23 is formed with an annular flange 25 and is biased by a spring 26 engaging the flange 25 toward the disc so that the head of the projecting portion 23 is normally in contact with the bottom 27 of the bore 24 of the first piston 5. An annular spring washer 28 fitted in an annular groove formed on the first piston at a position adjacent to the open end of the bore 24 is provided for receiving the reaction of said spring 26.

The operation of the friction pad pressing apparatus of the present invention is as follows.

When a substantially equal amount of working fluid is normally supplied to the cylinder from the first and second hydraulic pressure circuits respectively, the first piston acts to press the friction pad 3 against the disc under the influence of the hydraulic pressure acting on the whole diametrical area of the first piston. The second piston 6 has the same diametrical sectional area as the first piston 5 and the whole diametrical area of the former is subjected to the second hydraulic pressure introduced from the second hydraulic pressure circuit which acts to urge the second piston to the left. However, since the whole diametrical area of the left-hand side surface of the second piston receives the first hydraulic pressure introduced from the first hydraulic pressure circuit which acts to urge the second piston to the right, no displacement of the second piston due to either of the first and second hydraulic pressures occurs under such a condition that the first and second hydraulic pressures are equal with each other. Therefore, the second piston will be moved to the left with the forward end thereof being maintained in contact relation with the bottom 27 of the bore 24 so long as the resultant pressing force acting on the second piston to the right due to the difference between the pressing force acting on the second piston exerted by the first hydraulic pressure and the same exerted by the second hydraulic pressure is not larger than the resilient force exerted by the spring 26 through which the second piston 6 is engaged by the first piston 5.

As the friction pad 3 wears and its thickness is reduced, both the first piston and the second piston are advanced to be positioned at a forward position, while being prevented by the detent device for the second piston from being retracted rearwardly. The pressing force exerted by the second hydraulic pressure to act on the bottom 9 of the cylinder 4 is transmitted to an arm 29 integral with the cylinder and extending across the outer peripheral surface of the disc to support the friction pad 2, whereby the pad 2 is pressed against the disc.

in case the first hydraulic pressure circuit is impaired and does not supply the hydraulic pressure to the first liquid chamber, the first piston is not moved by the first hydraulic braking pressure, but is moved by the second piston which is actuated by the second hydraulic braking pressure to move to the left.

In this case, since the second piston and the first piston are maintained in engaged relation with each other by the resilient force of the spring 26, the disc can be braked only by the agency of the second hydraulic braking pressure acting on the second piston so as to press the friction pads 2 and 3 against the disc 1. Furthermore, in this case, substantially the same pressing force as was exerted by the first hydraulic pressure when the first hydraulic pressure circuit was effectively in operation is transmitted by the second piston to the first piston. Therefore, the operator of an automotive vehicle can effect the braking operation with substantially the same braking force as was available when both hydraulic pressure circuits were in the normal operation.

0n the other hand, in case the second hydraulic pressure circuit is impaired and does not supply the hydraulic pressure to the second liquid chamber, the first piston will be moved by the first hydraulic pressure as was the case when both hydraulic pressure circuits were effectively in operation, while the second piston is likely to be moved rearwardly to the right by the first'hydraulic pressure, but its movement to the right is restricted by the detent device. Therefore, while the first piston moves to the left, the second piston is maintained stationary with respect to the cylinder 4. At this time, the resultant force for pressing the first piston to the left which is the difference between the pressing force produced by the first hydraulic pressure and the resilient force of the spring 26 will act on the first piston. In this case, since the resilient force of the spring 26 is negligibly smaller than the pressing force acting on thefirst piston produced by'the first hydraulic pressure, the operator of an automotive vehicle caneffect the braking operation with substantially the same braking force as was available when both hydraulic pressure circuits were in the normal operation.

More particularly, in this case, since the rightward movement of the second piston is restricted by the detent device, the pressing force exerted by the first hydraulic pressure so as to move the second piston to the right is transmitted to the arm member 29 through the detent device and the hydraulic cylinder, thereby pressing the frictionpad 2 against the disc.

As will be clearly understood from the description made hereinbefore with reference to the accompanying drawing, the detent device itself employed in thefriction pad pressing apparatus according to the present invention is known. However, the operation of the detent device is not only effective for compensating the wear of the friction pads, but also it enables the pressing apparatus of this invention to operate normally without requiring any additional supply of the braking liquid to the first hydraulic pressure circuit even when the second hydraulic pressure circuit is impaired.

Although the present invention has been described in connection with the embodiment which employs a caliper type disc brake, it should be noted that the present invention may be employed in a disc brake of opposed piston type wherein a pair of friction pads are adapted to be pressed against a rotating brake disc, and the same effect as in the case hereinbefore described can be obtained.

What we claim is:

1. A friction pad pressing apparatus for use in a disc brake operated by a dual hydraulic braking system in- S 6 cluding a first hydraulic pressure circuit and a second and connecting means between the first and second hydraulic pressure circuit and comprising, pistons so that in use the pistons move away from a cylinder, the said end of the cylinder substantially in unison a first piston slidable in the cylinder in liquid-tight rewhen the first and second hydraulic pressures are lationship therewith and arranged to be actuated in substantially equal. use by hydraulic pressure supplied by the first hy- 2. Apparatus according to claim 1 in which the condraulic pressure circuit so as to be pressed directly necting means includes resilient means urging the first against an associated pad disposed on one side of and second pistons into contact with each other.

a rotary brake disc, 3. An apparatus according to claim 2 in which the a second piston slidable in the cylinder in liquid-tight connecting means further comprises a bore in the first relationship therewith and arranged to be actuated piston, a projecting portion of the second piston which by the differential in the hydraulic pressures supis loosely received in the bore and abuts against the plied respectively from the first hydraulic pressure bottom thereof, a flange provided on the projecting circuit and from the second hydraulic pressure cirportion, and a spring washer adjacent the open end of cuit, the bore, the resilient means being located on the prothe hydraulic pressure from the second hydraulic jecting portion and compressed between the flange and pressure circuit acting against the first hydraulic the spring washer, there being a clearance between the pressure on a cross-sectional area of the second flange and the bore of the first piston, and the head of piston equal to the cross-sectional area on which the projection portion being formed into a convex the first hydraulic pressure acts on the second pisshape.

ton, the cross-sectional areas each being equal to 4. Apparatus according to claim 1 in which the conthe cross-sectional area of the first piston on which nectingmeans comprises a bore in the first piston, a the first hydraulic pressure acts, projection of the second piston which is received in the detent means provided between the second piston bore and abuts against the bottom thereof, a flange proand the adjacent end of the cylinder and arranged vided on the projecting portion, a spring washer proto prevent the second piston from moving toward vided adjacent the open end of the bore, and resilient the said end of the'cylinder when the first hydraulic means located on the projecting portion and compressure is greater than the second hydraulic prespressed between the flange and the spring washer. Sure s =0: =1: s: 

1. A friction pad pressing apparatus for use in a disc brake operated by a dual hydraulic braking system including a first hydraulic pressure circuit and a second hydraulic pressure circuit and comprising, a cylinder, a first piston slidable in the cylinder in liquid-tight relationship therewith and arranged to be actuated in use by hydraulic pressure supplied by the first hydraulic pressure circuit so as to be pressed directly against an associated pad disposed on one side of a rotary brake disc, a second piston slidable in the cylinder in liquid-tight relationship therewith and arranged to be actuated by the differential in the hydraulic pressures supplied respectively from the first hydraulic pressure circuit and from the second hydraulic pressure circuit, the hydraulic pressure from the second hydraulic pressure circuit acting against the first hydraulic pressure on a crosssectional area of the second piston equal to the crosssectional area on which the first hydraulic pressure acts on the second piston, the cross-sectional areas each being equal to the cross-sectional area of the first piston on which the first hydraulic pressure acts, detent means provided between the second piston and the adjacent end of the cylinder and arranged to prevent the second pIston from moving toward the said end of the cylinder when the first hydraulic pressure is greater than the second hydraulic pressure, and connecting means between the first and second pistons so that in use the pistons move away from the said end of the cylinder substantially in unison when the first and second hydraulic pressures are substantially equal.
 2. Apparatus according to claim 1 in which the connecting means includes resilient means urging the first and second pistons into contact with each other.
 3. An apparatus according to claim 2 in which the connecting means further comprises a bore in the first piston, a projecting portion of the second piston which is loosely received in the bore and abuts against the bottom thereof, a flange provided on the projecting portion, and a spring washer adjacent the open end of the bore, the resilient means being located on the projecting portion and compressed between the flange and the spring washer, there being a clearance between the flange and the bore of the first piston, and the head of the projection portion being formed into a convex shape.
 4. Apparatus according to claim 1 in which the connecting means comprises a bore in the first piston, a projection of the second piston which is received in the bore and abuts against the bottom thereof, a flange provided on the projecting portion, a spring washer provided adjacent the open end of the bore, and resilient means located on the projecting portion and compressed between the flange and the spring washer. 